Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

2. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

3. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

4. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

5. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

10°C

5°C

6. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

7. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Reversed Carnot

Carnot

8. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Normal cooling

Super-cooling

9. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

10. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Always less than unity

Any one of the above

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11. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

Condenser tubes

12. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

13. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

14. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Room air conditioners

Domestic refrigerators

15. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

16. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

17. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

Condenser and receiver

18. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-135.8°C

-77.7°C

19. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

20. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Piston type reciprocating

Miniature sealed unit

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21. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

15 bar

2 bar

22. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 3

1: 9

1: 1

23. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

Any value

High

24. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

25. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

26. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.6

0.376

27. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

28. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

29. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

Above critical temperature

30. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

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31. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Positive

Zero

32. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

33. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

34. Which of the following cycles uses air as the refrigerant?

Carnot

Ericson

Stirling

Bell Coleman

35. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

36. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

37. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

4.33

1.33

38. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

39. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

40. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Carbon dioxide

Ammonia

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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